Updated shortcodes for unsubscribe/manage/browser links

- fixed all issues in #387 except the custom mailpoet pages

lib/Newsletter/Shortcodes/Categories/Subscription.php

@@ -0,0 +1,48 @@
+<?php
+namespace MailPoet\Newsletter\Shortcodes\Categories;
+use MailPoet\Subscription\Url as SubscriptionUrl;
+
+class Subscription {
+  /*
+    {
+      text: '<%= __('Unsubscribe') %>',-
+      shortcode: 'subscription:unsubscribe',
+    },
+    {
+      text: '<%= __('Manage subscriptions') %>',
+      shortcode: 'subscription:manage',
+    },
+   */
+  static function process(
+    $action,
+    $default_value = false,
+    $newsletter = false,
+    $subscriber = false
+  ) {
+    switch($action) {
+      case 'unsubscribe':
+        return '<a target="_blank" href="'.
+          esc_attr(SubscriptionUrl::getUnsubscribeUrl($subscriber))
+          .'">'.__('Unsubscribe').'</a>';
+      break;
+
+      case 'unsubscribe_url':
+        return SubscriptionUrl::getUnsubscribeUrl($subscriber);
+      break;
+
+      case 'manage':
+        return '<a target="_blank" href="'.
+          esc_attr(SubscriptionUrl::getManageUrl($subscriber))
+          .'">'.__('Manage subscription').'</a>';
+      break;
+
+      case 'manage_url':
+        return SubscriptionUrl::getManageUrl($subscriber);
+      break;
+
+      default:
+        return false;
+      break;
+    }
+  }
+}